The present invention relates to a gas injector for molding plastic hollow parts in an injection mold.
The injector includes a housing with a hollow enclosure or cavity within the housing.
The injector of the invention includes a tube connected through the hollow enclosure with a source of pressurized gas. The tube is designed to open out at its end into the cavity of an injection mold for molding plastic material to cause swelling of the plastic material and for making a hollow molded part. At that open end, the tube forms the seat of a sealing valve. The valve has a rod that extends inside the tube. A spring acting on the rod effects closure of the valve against the seat. This rod is also subject to the action of a type of motor means which are equipped with control means to open the valve against the spring force.
According to another feature of the invention, the spring is mounted in the enclosure or the cavity to surround the rod. One end of the spring bears against a cup which is integral with the rod and the other end bears against an end of the cavity.
The motor means comprises an electromagnet with a solenoid plunger. The electromagnet mounted at the other end of the enclosure from the valve causes the plunger to act axially on the rod to open the valve against the spring force.
Accordingly, the present invention has for its object the production of a gas injector with reliable operation, and particularly without the danger of the injection tube becoming clogged with plastic material that might flow back into the injection tube. Such flow back would in each case require the molding machine to be stopped causing loss of productivity associated with the time spent on taking down, cleaning and replacing the injectors.
Correct operation of the injector without clogging, even only without partial clogging, also produces better quality molded parts and assures constant quality. This substantially reduces the number of defective parts, which might have to be scrapped.
The improvement results from the fact that the injector of the invention makes it possible to bring a volume of gas that is constant from one operation to the next into the cavity of the mold within a specific period. This enables production of a hollow part of specific volume and shape to be repeated from one hollow part to the next, without the plastic part presenting local wall areas of a thickness that is abnormally too thin or too thick. This would create areas of too rapid cooling or too slow cooling on the part, resulting, at the very least, in appearance faults of the molded part.